1. Field of the Invention
This invention relates to a liquid flow controller and more particularly, to a multiport metering pump that can deliver a small quantity of liquid.
2. Description of Related Arts
Accurate control of liquid delivery is required in many industrial equipment for chemical analysis and process control applications. Thus, a number of methods for accurate delivery have been developed for industrial purposes.
A liquid flow controller employs a sensor to measure flow rate of a liquid. The sensor informs a servo valve of the flow rate, and then the servo-valve adjusts the flow rate. Describing the process in more detail, the sensor utilizes a diode emitting infrared light, a photo diode detecting light, and a Pelton type turbine wheel to determine the flow rate of the liquid. Light from the diode is alternately reflected and absorbed from spokes deposited on the turbine wheel, and energy of the reflected light is detected by the photo diode. Thus, as the turbine wheel rotates in response to flow rate, electrical pulses are generated. According to the electrical pulses, processing circuitry provides a DC voltage output proportional to the flow rate. Then, a bi-directional linear stepper motor moves a micro-flow control valve of the servo valve in response to any difference between the desired flow and the actual flow rate.
Another liquid flow controller employs a variable stroke electromagnetic valve featuring a valve seat design which permits increasing or decreasing the flow rate of a liquid in response to variable input power. Input power generated from a flow rate detector is intermittently applied to a valve coil of the electromagnetic valve. When the input power is applied, energy in the coil increases, and when it is discontinued, energy stored in the coil maintains the magnetic flux level required to hold flow at a controlled rate. This cycle takes place many thousands of times per second. By using a variable DC power supply, the valve opening can be adjusted proportional to the supplied power.
The above-described controllers may precisely control the flow rate of a liquid, delivering the liquid from a container connected to an inlet port of the controllers to another container connected to an outlet port of the controllers. However, in particular cases, a liquid flow controller may need to deliver various kinds of liquids contained in different containers. Accordingly, such particular applications demand a liquid flow controller to have multiports for delivering various liquids, each port of the multiports can be used as an inlet or outlet port.
The present invention is directed to a multiport metering pump that can completely deliver a very small volume of liquid. The multiport metering pump includes a number of ports (or valve units), each of which can be used as either an outlet valve or an inlet valve.
In accordance with an embodiment of the invention, the multiport metering pump includes: a central gallery; a displacement unit; multiple valve units; and multiple conduits that respectively connect the displacement unit and the valve units to the central gallery. The displacement unit and the valve units communicate with the central gallery, and any of the valve units can be used as an inlet valve or outlet valve for the liquid delivery.
The displacement unit includes: an upper body; a lower body; a displacement unit diaphragm which is sealed between the lower body and the upper body so as to form a displacement unit cavity; and a conduit port. The conduit port is formed in the lower body so as to allow the liquid to flow between the displacement unit cavity and the central gallery through one of the conduits. The displacement unit diaphragm moves up and down so as to open and close the conduit port. The displacement unit diaphragm is in a disk shape. The middle portion of the displacement unit diaphragm is thin and flexible so that the central portion of the displacement unit diaphragm can move up and down so as to open and close the conduit port while the outer portion of the displacement unit diaphragm is fixed between the upper body and the lower body.
The displacement unit further includes a circular groove around the open cavity of the lower body, an actuator, and a securing screw piston. The outer portion of the displacement unit diaphragm sits in the circular groove, and the actuator piston drives the displacement unit diaphragm to move up and down. The securing screw connects the actuator piston to the displacement unit diaphragm.
Each of the valve units includes: an upper body; a lower body; a valve unit diaphragm which is sealed between the lower body and the upper body to form a valve unit cavity; an inlet/outlet port; a conduit port; and a valve seat formed around the conduit port. The valve unit diaphragm moves up and down so as to open and close the conduit port. Through the inlet/outlet port, liquid flows between the valve unit cavity and an external container connected to the valve unit. The conduit port is formed in the lower body so as to allow the liquid to flow between the valve unit cavity and the central gallery through one of the conduits
The valve seat is in a conical shape, and the valve unit diaphragm includes: a central portion; a middle portion that surrounds the central portion; and an outer portion that surrounds the middle portion and is fixed between the upper body and the lower body. The central portion is in a hemispherical shape so as to fit in the conical valve seat to seal the valve unit cavity from the conduit port. The middle portion is thin and flexible so that the central portion can move up and down so as to open and close the conduit port while the outer portion is fixed between the upper body and the lower body.
Each of the valve unit further includes a circular groove around the open cavity of the lower body, an actuator, and a securing screw piston. The outer portion of the valve unit diaphragm sits in the circular groove, and the actuator piston drives the valve unit diaphragm to move up and down. The securing screw connects the actuator piston to the valve unit diaphragm.
In addition, the actuator pistons of the valve units and the displacement unit are driven by a pneumatic system. The upper bodies, the lower bodies, and the diaphragms of the valve units and the displacement unit are made of PTFE Teflon(trademark).